Ohm-meter.



H. G. STUART,

OHM METER.

APPLICATION FILED FEB. 24.191?.

1,275,786, Patented Aug. 13, 1918A M ff l i l'@ I Il (l l' il r UNITED sTATns PATENT OFFICE.

HARRY GOULD STUART, 01* PATERSON, NEW JERSEY.

0HMMETER.

To all 'whom it may concern.'

Be it known that l, HARRY G. STUART, a citizen of the United States, and a resident of Paterson, in the county of Passaic and State of New Jersey, have invented a new and. improved Olim-Meter, of which the following is a full, clear, and exact description.

This invention relates to electrical measuring instruments, and more particularly to a irect reading ohm-meter.

yThe invention has for its general objects 4to provide an improved electrical measuring instrument of the character referred to which embodies an ammeter and a voltmeter arranged 1n a speclal manner and having respectively a movable dial and a hand or indicator so correlated to the dial that by'means of the two it is possible to read directly the resistance of a conductor to be measured, the instrumentbeing'of comparatively si-mple and inexpensive construction,.

unitary or self-contained, requiring only connections with a cell or other source of current and a' conductor of unknown resistance to be measured, and being direct reading it eliminates the necessity of two readings according to the old ammeter and voltm'eter method and the computation based on lowing description and claims taken in con- On the casing are bindinposts 5 andv 6 for ctor whose resist-` nection with the accompanying drawing, in which 'similar characters 4of reference indicate corresponding parts inboth the views, and in whichhi Figure 1 is a meter; and

Fig. 2 isa diagrammatic view. Referring to the drawing, 1 designates a casing of any suitable character "which has perspective view of the ohm- .a glazed opening 2 through which is re,

vealed a scale 3 and a hand or indicator. 4.

connection with the cond,

Specification of Letters Patent.- Patented Aug, 13, 1918, Application filed ebruary 24, 1917. Serial No. 150,721'.

ance is to be measured, and also on the casing are binding'posts 7 and 8 which are adapted to be connected with cells or other source of current. On the outside of the casing is a rheostat lever 9 which is ada ted to be moved over a. series of contact liuttons 10. A

Within the casing is an ammeter unit A and a'voltmcter unit B. The movable element 11 of the ammcter carries or ioper atively connected with the scale or dial 3,

the same being in thc form of' an arm extending from the movable element of the ammeter.` The movable element 12 of the voltmeter carries or is operatively connected with the hand or indicator 4, which extends from the.Y movable element 12 in a direction approximately at right-angles to the scale-carrying arm of the ammeter. Normally the scale 3, when inv zero posit-ion,

is farthest away from the voltmeter, and` as the ammeter is energiaed thescale moves toward the voltmeter. Normally the indicator l is, when in zero position, close to the ammeter, and when the volhncter is energized the indicator moves away from the ammeter. Thus the 4scale and indicator overlap, and by thc position of the indicator with respect to the dial'or scale, the

ohmic value of a. conductor to be measured can be immediately seen by nie-ans ofthe curves or lines on the scalev and the Immerals associated therewith.

The winding 13 of the alnmeter is in series with the cell or source of current and the conductor, (l, the resistance of which is to 'be measured, and parallel with the winding 13 is a shunt 14. Oneterminal 'of the winding 13 is connected with the lever 9` of the rheostat, which lever is normally held in open circuit position "by a spring 15. ,The contact buttonsof the rheostat are connected with the binding posts 8, so that the rheo stat ,is in series with the cell. When `the lever 9 is mved to the right, any amount of resistance can lbe introduced. Thepurpose of the rheostat is two-fold. First, it protects the instrument from the effects of excessive currents, and second, 'in lcase the i value of the resistance to be measured is such that, without any Vexternal resistance either the ammeter dial orjvoltmeter indicator, or both, should be moved beyond the i maximum point, the rheostat by means'of its gradually" decreasing resistance, increases `tho ronduetor (l.

the current. How gradually, than bringing bot-l1 ammeter dial and voltmeter indiator slowly trom a zero posit-ion to a point-ot' maximum aeeuraey. lt mui-1t. be borne in mind that the introduetion of this external resistant-.e will n ot. alfeet the relation of the eurrent tlow through the eonduetor to the potential ditt'ereneebetween the extremiti'ea ot' the condnetor. 150th quantities will inerease in the `same ratio. The ohm-meter` .measuring a ront-:tant relation between the eurrent flow through the eonduetor and the potential difference between it extremities, will be nnatleeted by the introduction of an external resistance not ineludecl between the, points. i

'lhe winding 16 of the voltmeter'is conne'eted in parallel with the conductor and in series with the coil 16 is tho volt-meter ro- .sistanee 1T. lty will be understood that when the eireuitiis'eloaed 'the coils 13 and 1t; of the alnmeter andvoltmeter will be energized and the dial 3 and indicator l will move simu]tzaneouslv, and when theyveome to rest they will indicate in ohms the resiSt-anee. of

From the t'oregoinrr deseription taken in ('.ouneetion with the aeeolnpanying drawing.-

the. advantagea ot the eonstruetion and method ot' operation will be readily understood b v those Skilled in the art to whieh the invention appertains` and while l have deseribed the prineiple of operation.'y bogethervwith the apparatus whieh l now con- `aider to be the beat. emlmdimentI thereof` I desire to have it. understood that the apparatusA Ahown is merel \Y illuatrative and that lsneh rhangeS may be made when de., \.ired'as :tial and hand extemlinr,r ap}')roximately at right-angles to eaeh other when in zero position.

1.. A direet reading ohm-meter compris ing a voltmeter yunit` an ammeter unit7 each unit. having a movable element, a dial on the movable element of the ammeter, and a haul eonnerted with the movable. element of the voitmeter and movable over the dial, said dial and hand extending approximately at right-angles to eaeh other when in zer-o position. i

Il. direet readingr ohm-meter eomprining an. ammeter unit: a voltmeter u'nit. said unitivv havingr movable elementzw'. a Swingin@ dial earried by the movable element of the' ammeter unit. and a Swinging indieator tarried by the movablev elementl of the voltmeter unit and havingv it# length approxiniatelr' a right-angles to the length oi the dial. miti dial having rurver` with whieh the indi- -eator eoiperates to indieate in terms of ohmmI the resistanro of the element to be measured and the curve at zero being approxinaiteiy (,foneentrie with the axis of movement and the eurve sneeessivetv ehangingg in angle to approxinnitel)Y a radial position at the. opposite. limitof the sealev from zero.

l. A dial 'for a direetreading ohm-meter 'adapted to swiifig about an axis and havii j a `series ot' curves. the zero Curve being' aL -1 proximatelveonoentrir :with the axis oz" movement. and the. curves4 surewsiveljr ehanging in 'angle to approximately a radial position at thel opposite limit of the aeaie from zero.

5. A dial foria direet reading olmi-nieter adapted to swing about an axis and having a series of curves. the zero curve being" approximately eoneentriel with theI axis of movement. and the curves sueeesively ehangingin angle to approximately a radial position at the oppositelimit ot the scale from zero` an ampere @reale on one edge of the dial and concentric with the zero curve, and a volt .Qt-alo on the dial atrnek from a radium` at approximately right-angles from the radius from whieh the ampere seule is struck.

HARRY GOUL'D S'. UARR 

